Field of the Invention
This invention relates to guided gun-launched munitions and more specifically to a multi-function radio frequency (MFRF) module that provides active and semi-active terminal guidance and fuzing sensors for gun-launched munitions.
Description of the Related Art
Gun-launched munitions are projectiles that are provided an initial velocity at launch (e.g. conventional gun powder or electromagnetic rail gun) and whose trajectory is subsequently governed by the laws of classical mechanics. Most gun-launched munitions achieve ballistic stability by spinning at a high rate. The rifling of the gun barrel imparts a spin to the munition when fired. The spinning projectile is stabilized by gyroscopic forces that resist perturbations. Other unguided munitions have airfoils that stabilize the munition's trajectory. The airfoils move the center of pressure of the munition aft of its center of gravity providing a static stability margin. The airfoils are also canted to impart a low spin rate, which minimizes the affects of non-uniform fabrication tolerance buildup.
These weapon systems are typically “fire and forget”. The system computes a firing solution based on a ballistic trajectory to intercept the target. The firing solution is based on the best information available about the target (e.g. range, speed, direction), the environment (e.g. temperature, wind conditions etc.) and the projectile itself. The accuracy of such systems is limited by this knowledge and environmental stability.
Some gun-launched munitions provide for post-launch guidance of the munition. For sensor stability, guided munitions have a low to zero spin rate. Tail fins that are folded and deploy upon exiting the gun barrel provide stability and low-level spin control. Fine spin control and guidance control can be provided by the tail fins or a separate actuator such as canards, wings, reaction jets or impulse thrusters. These munitions are of “full caliber” having a maximum diameter equal to that of the barrel and tapering down to the front of the munition.
Raytheon Missile System has fielded a 155 mm extended range guided artillery shell known as the “M982 Excalibur”. The M982 Excalibur uses GPS guidance and foldable airfoils that deploy upon leaving the barrel to guide the munition to pre-programmed GPS coordinates. The M712 Copperhead is a 155 mm caliber cannon-launched, fin-stabilized, terminally laser guided, explosive projectile intended to engage hard point targets such as tanks or self-propelled howitzers. Italian defence company Oto Melara has developed a 76 mm gun that fires a Driven Ammunition Reduced Time of Flight (“DART”) muntion. The guidance system is Command Line of Sight (CLOS) from a transmit antenna on the gun to a data link antenna on the rear of the DART munition.
Some large caliber munitions such as the 155 mm (6.1 inch) munition contain an additional fuze assembly. The fuze assembly may include a mechanical sensor to detect impact, an electrical sensor to measure elapsed time or time delay or an RF sensor to measure Doppler/Doppler rate for proximity detonation or range-to-target for a Height of Burst detonation. The RF sensor includes a forward facing antenna and an RF transmitter/receiver to measure RF reflections off of the target to compute the Doppler/Doppler rate or range-to-target. In guided munitions, the fuze assembly is physically separate from and operates independently of the seeker and guidance assemblies. The fuze assembly must meet stringent safety requirements that preclude software. All fuze logic is implemented in firmware.